264 ELEMENTARY PHYSIOLOGY less. 



The contents of the small intestitie, thus white and 

 milky, are sometimes called chyle ; but it is best to reserve 

 this name for the contents of the lacteals, of Avhich we 

 shall have to speak directly. 



The emulsification and saponification of the fats are not, 

 however, the only changes going on in the small intestine. 

 The pancreatic juice has an action on starch similar to 

 that of saliva, but much more powerful. During the 

 short stay in the mouth veiy little starch has had time to 

 be converted into sugar, and in tlie stomach, as we have 

 seen, the action of the saliva is arrested. In the small 

 intestine, however, the pancreatic juice takes up the work 

 again ; and indeed, by far the greater part of the starch 

 which we eat is digested, that is, changed into maltose, by 

 the action of this juice. A ferment in the succus 

 entericus converts the maltose (Ci2H,20ii) into dextrose 

 (CgHj-jOg) in which form the sugar is absorbed. 



Nor is this all, for, in addition to the above, the alkaline 

 pancreatic juice has a powerful effect on proteins very 

 similar to that exerted by the acid gastric juice ; it con- 

 verts them into peptones, and the peptones so produced 

 do not differ materially from the peptones resulting from 

 gastric digestion. At the same time a variable amount of 

 leucine, tyrosine, and other amino-acids make their 

 appearance as the result of the further action of pan- 

 creatic juice on the first-formed peptones. Here again 

 the succus entericus aids digestion. Peptone if absorbed 

 into the blood would act as a deadly poison. A ferment 

 erepsin also breaks up the peptone into a number of much 

 simpler bodies known as amino-acids. These are com- 

 plicated organic acids which however contain nitrogen in 

 a form closely related to the nitrogen in ammonia and 

 urea. 



Hence it appears that, while by the saliva carbo- 

 hydrates only, and by the gastric juice i)roteins only, are 

 digested, in the intestine all three kinds of food-stuffs, 

 proteins, fats, and carbohydrates, are completely dis- 



